1. Field of the Invention
The present invention relates to a drill for forming undercuts in cylindrical bores formed in stone or concrete and including a drilling member having a stem provided, at one of its longitudinal ends, with a shank receivable in a chuck of a hand-held drilling tool and, at another of its longitudinal ends, with a cutting head with abrasive cutting bodies, and a sleeve for receiving the drilling member and having, at its end adjacent to the shank, a radial collar and a drag bearing arranged inside the sleeve for supporting the drilling member.
2. Description of the Prior Art
For attachments of constructional parts subjected to high tensile loads, in particular for safe attachments, often formlocking anchoring of the fastening elements is used. With the formlocking anchoring, the generation of expansion forces, upon application of a load, is prevented to a most possible extent. With the formlocking anchoring, smaller than with conventional anchoring, distances between axes and edges can be maintained. With the formlocking anchoring, undercut-engaging anchors, which usually have an anchor rod with a head portion widening in a setting direction and a sleeve axially displaceable over the anchor rod, are used. At its end adjacent to the head portion of the anchor rod, the sleeve has a plurality of expansion tabs which expands radially upon displacement of the sleeve over the head portion and which engage in a preliminary formed undercut, forming a formlocking connection with the bore wall.
For forming an undercut in a preliminary formed substantially cylindrical bore in stone or concrete, a drill such as disclosed, e.g., in German Patent No. 3,143,462, is used. The drilling member of the drill has, at one of its end, a shank receivable in a chuck of a hand-held drilling tool, and, at its opposite end, a cutting head with abrasive cutting bodies. The drilling member is supported by a drag bearing in a sleeve provided with a radial collar for supporting the drill on the edge of a bore. The drag bearing is formed as a radial circular projection extending from the inner wall of the sleeve and spaced from the collar. During the formation of the undercut, the drilling member performs stirring movements. The abrasive cutting bodies on the cutting head cause disintegration of the bore wall, forming more or less fine particles and fragments. During formation of undercuts in horizontal bores or in overhead bores, the comminuted particles and fragments can reach the sleeve and be retained there, preventing the pivotal movement of the drilling member. This makes the formation of an undercut more difficult or even impossible.
Accordingly, an object of the present invention is to provide a drill for forming an undercut in which the drawbacks of the known drill are eliminated.
Another object of the present invention, is to provide a drill for forming undercuts and which can be used simply and reliably.
These and other objects of the present invention, which will become apparent hereinafter, are a achieved by providing a drill for forming undercuts in cylindrical bores formed in stone or concrete and including a drilling member having a stem provided, at one of its longitudinal ends, with a shank receivable in a chuck of a hand-held drilling tool and, at another of its longitudinal ends, with a cutting head with abrasive cutting bodies. The drill is supported in a drag bearing inside of sleeve having a through-bore and, at its end adjacent to the shank, a radial collar.
The sleeve has at least one through-opening formed in a front, in a direction toward the cutting head, section of the sleeve and spaced axially from the drag bearing by a distance amounting to from about 0.05xc3x97D to about 0.6xc3x97D, preferably, from 0.2xc3x97D to 0.4xc3x97D, where D is an outer diameter of the sleeve in the region of the drag bearing.
The selected location of at least one opening insures that no drillings or drilling dust reaches the region of the drag bearing. The drillings or fragments, which reach the sleeve during horizontal or overhead formation of an undercut, fall out through the through-opening. The sleeve would not be filled with drillings or fragments which can hinder the undercut-forming process. The drilling dust, which adheres to the inner wall of the sleeve, can be loosened by knocking on the sleeve and exit through the through-opening. The drill has a simple construction and does not differ in its main function from the conventional drills. Thus, the user need not familiarize himself with a new technique.
Advantageously, the at least one through-opening has an axial length which is larger than an opening width in a circumferential direction of the sleeve. The axial length of the through-opening amounts to from 0.05xc3x97L to 0.5xc3x97L, preferably, from 0.1xc3x97L to 0.4xc3x97L. L is an operational length of the drill defined by a distance from the radial collar to an end of the sleeve adjacent to the cutting head. The through-opening width amounts to from 0.1xc3x97D to 0.7xc3x97D, preferably from 0.2xc3x97D to 0.5xc3x97D. At these dimensions, a reliable removal of the formed concrete particles from the sleeve is insured.
According to one of the embodiments of the invention, the sleeve has a plurality of through-openings arranged axially one after another in the sleeve front section. The openings extend over a length of the sleeve which is larger than an opening width in a circumferential direction of the sleeve. This length amounts to from 0.05xc3x97L to 0.5xc3x97L, preferably from 0.1xc3x97L to 0.4xc3x97L, where L is an operational length of the drill defined by a distance from the radial collar to an end of the sleeve adjacent to the cutting head. The opening width amounts to from 0.1xc3x97D to 0.7xc3x97D, preferably, from 0.2xc3x97D to 0.5xc3x97D.
To improve the removal of drillings, a plurality of through-openings are distributed over the sleeve circumference. The through-opening can have the same shape. However, advantageously, the through-openings have a different geometry to take into account different sizes of drilling particles and fragments. The removal of the drillings can further be improved when a limiting surface of a through-opening adjacent to the drag bearing has a chamfer. The chamfer guides the drilling outside.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred. embodiments, when read with reference to the accompanying drawings.